Questions tagged [coordinate-system]

A reference framework consisting of a set of points, lines, and/or surfaces, and a set of rules, used to define the positions of points in space in either two or three dimensions. This tag also refers to cartographic projections and coordinate system transformations.

Filter by
Sorted by
Tagged with
263 votes
11 answers
153k views

Difference between projection and datum

What is the difference between a projection and a datum?
fmark's user avatar
  • 9,381
248 votes
4 answers
273k views

EPSG 3857 or 4326 for Web Mapping

The discussion at What is the difference between WGS84 and EPSG4326? shows that 4326 is just the EPSG identifier of WGS84.. Wikipedia entries for Google Maps and OpenStreetMap shows that they both ...
tmaj's user avatar
  • 2,593
189 votes
5 answers
229k views

Difference between WGS84 and EPSG:4326

What is the difference between WGS84 and EPSG 4326? It seems like for a given dataset it might be both WGS84 and EPSG:4326.
Alex B's user avatar
  • 2,246
176 votes
8 answers
290k views

Algorithm for offsetting a latitude/longitude by some amount of meters

I'm looking for an algorithm which when given a latitude and longitude pair and a vector translation in meters in Cartesian coordinates (x,y) would give me a new coordinate. Sort of like a reverse ...
Thomas O's user avatar
  • 2,053
125 votes
4 answers
523k views

Does Y mean latitude and X mean longitude in every GIS software?

I am using Mapinfo and it has Y as latitude and X as longitude. Is that the same case for all mapping software? As for any country their respective value is multiple of 1 or -1. So for Nepal can I say ...
kinkajou's user avatar
  • 4,406
108 votes
16 answers
74k views

Identifying Coordinate System of Shapefile when Unknown?

I have a Shapefile but its coordinate system is Unknown, and there is no *.prj file. How can I identify it now?
com's user avatar
  • 3,694
93 votes
10 answers
231k views

Converting projected coordinates to lat/lon using Python

This site returns Point: X: -11705274.6374 Y: 4826473.6922 when you search with the first key value of 000090, as an example. I assume that this is a spatial reference. I am looking for instructions, ...
Vincent's user avatar
  • 1,041
84 votes
5 answers
46k views

Displaying coordinates and inputs as LatLon or LonLat?

I'm trying to get a sense if this is an issue for others or every input/output should be labeled so user is not confused and just go with it? I think almost everyone pronounces it as "LatLon". Who ...
77 votes
2 answers
22k views

How accurate is approximating Earth as sphere?

What level of error do I encounter when approximating the earth as a sphere? Specifically, when dealing with the location of points and, for example, the great circle distances between them. Are ...
Jeff B's user avatar
  • 935
72 votes
1 answer
64k views

Choosing SRID and what is its meaning? [closed]

I'm new to GIS, in PostGIS, and I'm struggling with the SRID concept. How do you choose a SRID for a database column? This is making me crazy. Why do I need to choose a SRID? What's its meaning? ...
bluish's user avatar
  • 901
66 votes
3 answers
95k views

Layers with same coordinate system should align/overlap in ArcMap but do not?

I put 4 different layers into my ArcMap document, but only one of them will show up on the map! I should be seeing the other 3 layers as well. When I do a Zoom to layer, I can see one layer, but I ...
CaliforniaGirl's user avatar
64 votes
7 answers
10k views

What strategies, criteria, or rules to use for selecting coordinate systems?

What strategies, criteria, or rules do you use for selecting coordinate systems for (a) storing, (b) analyzing, and (c) displaying GIS data? (I humbly offer my reply to a related question about ...
whuber's user avatar
  • 69.8k
63 votes
3 answers
59k views

Changing SRID of existing data in PostGIS?

While importing my shapefile data to PostGIS, I did not select the proper Projection. How do I now change the SRID of the data, without transforming the Coordinates?
Devdatta Tengshe's user avatar
60 votes
6 answers
6k views

One dimensional map of the world?

Bit of a strange question but hope this is OK to ask here. Has anyone heard of a '1-dimensional' projection of the world map - that is mapping all the points on the globe to a single line? I was ...
utunga's user avatar
  • 883
59 votes
6 answers
41k views

Why is the 'straight line' path across continent so curved?

This is the result of mapping the straight line path from a point in US to Poland using Distance Measurement Tool. Also, planes from Asia to US would travel almost over North Pole. Why is the path ...
Lazer's user avatar
  • 701
58 votes
7 answers
165k views

Getting list of coordinates for points in layer using QGIS?

I've got a layer in QGIS that is comprised of points. Its attribute table doesn't have (show) the corresponding x and y coordinates for each point. Is there a way for me to extract a list of ...
hpy's user avatar
  • 3,157
56 votes
4 answers
16k views

Why has Web Mercator (auxiliary sphere) become the web map standard?

I understand what the difference is between the Web Mercator projection and Web Mercator Auxiliary Sphere (WMAS). I also understand that both Google and Esri have adopted this projection as their ...
dkroy's user avatar
  • 1,368
55 votes
3 answers
57k views

Transforming Shapely Polygon and MultiPolygon objects

Is there an easy way of transforming Shapely objects (namely, Polygons and MultiPolygons) from one projection to another without having to dig around and extract coordinates by hand? In fact, I don'...
Chris Fonnesbeck's user avatar
53 votes
3 answers
73k views

Reprojecting vector layer in QGIS

I have a series of layers of lines (shapefiles) in My Project. The CRS of some are different and to merge them they all must have same CRS. When I use Processing > Toolbox > Qgis_algorithims >...
razi's user avatar
  • 531
49 votes
2 answers
49k views

What's the difference between EPSG:4326 and EPSG:900913?

I am a bit confused on EPSG:4326 and EPSG:900913. I thought that they were both same. Though as I am placing my features over GMaps, which is EPSG:4326, I need to define the srsname of the WFS layer ...
Sam007's user avatar
  • 4,395
47 votes
3 answers
24k views

Reprojecting all geometries in PostGIS table?

I created a spatial table with SRID:4326. Now I want to change total projection to SRID:32644 into a new table. The old table should remain unchanged.
Satya Chandra's user avatar
45 votes
2 answers
35k views

What is the difference between EPSG:900913 and EPSG:3857?

I'm using the QGIS google layers plugin to digitize a parcel as a shapefile. Later I want to import it to PostGIS. I know that google maps use a special 'google mercator' projection. What is the ...
Jiri Kadlec's user avatar
45 votes
3 answers
18k views

What is the current Web Mercator projection code?

The web mercator projection, popularised by Google Maps, seems to be given a new EPSG code every couple of years. EPSG:900913 (Google in calculator text) was an unofficial code EPSG:3785 - is the ...
geographika's user avatar
  • 14.3k
43 votes
2 answers
74k views

Projecting sp objects in R

I have a number of shapefiles in different CRSs (mostly WGS84 lat/lon) that I'd like to transform into a common projection (likely Albers Equal Area Conic, but I may ask for help on choosing in ...
Ari B. Friedman's user avatar
43 votes
5 answers
16k views

Reprojecting raster from 0 360 to -180 180 with cutting 180 meridian using gdalwarp

I have a geotiff raster image that has a coordinate system with longitudes from 0 to 360. The horizontal center of the image is 180 longitude. See image below: I want to transform it to EPSG:4326 SRS ...
nextstopsun's user avatar
  • 1,129
42 votes
1 answer
23k views

Is WGS84 itself a Coordinate Reference System?

I was wondering the difference between WGS84 and EPSG:4326 (see this). Can then WGS84 on its own be defined as a Coordinate Reference System? Or is it just a datum so that a Coordinate System must ...
Campa's user avatar
  • 785
42 votes
1 answer
9k views

Coordinate system for accurately calculating areas of polygons that cross UTM Zones?

I have multiple polygons, all located offshore around the UK. I am trying to calculate the areas of these polygons in square kilometres, without splitting them by UTM zone. Is it possible to do this ...
the_bonze's user avatar
  • 817
41 votes
6 answers
24k views

Shapefile PRJ to PostGIS SRID lookup table?

I was wondering if there is such a thing as an shapefile PRJ to PostGIS SRID lookup table? Something that can translate the most standard shapefile PRJ definitions into the likely SRID. When using ...
RyanKDalton's user avatar
  • 23.1k
41 votes
1 answer
24k views

Defining new custom projections in QGIS?

I'm trying to define a projection in QGIS. I want to add North America Albers Equal Area Conic. From the spatialreference site I copied the proj4 line: +proj=aea +lat_1=20 +lat_2=60 +lat_0=40 +lon_0=-...
djq's user avatar
  • 16.3k
39 votes
1 answer
43k views

What is the default projection in Leaflet?

I've read an API documentation for Leaflet on its site, but I can't realize: what is a default projection to view maps? It was written about spherical and elliptical Mercator and Equirectangular - so ...
Anton's user avatar
  • 491
38 votes
3 answers
18k views

What is approximate error of Pythagorean Theorem vs. Haversine Formula in measuring distances on sphere at various scales?

Many people when first trying to calculate distances between two longitude / latitude pairs ask if Pythagorean theorem works as an appropriate distance function. Most often people answer "no, the ...
Amos Budde's user avatar
37 votes
8 answers
43k views

How do I convert State Plane coordinates to latitude-longitude?

Given a specific state plane coordinate system (whether NAD27 or NAD83), are there any resources to convert to latitude-longitude?
Richard Morgan's user avatar
37 votes
4 answers
8k views

What was the rationale for the non-standard UTM zones near Norway?

UTM zones 30V, 31V, 32V, 31X, 33X, 35X, and 37X do not line up with the rest of the UTM zone grid. Why was this allowed? According to Wikipedia, UTM was developed by the U.S. Army Corps of Engineers ...
Jaime Soto's user avatar
  • 1,393
37 votes
2 answers
4k views

Choosing coordinate system to store geography data for celestial coordinates

I am doing an astronomy project. I want to have the information about our images stored in a spatially enabled database. This, I would think, should be a very easy special case for GIS functions ...
SO Stinks's user avatar
  • 473
35 votes
3 answers
5k views

Why are Data Projections relevant?

Why is it useful to store data in unusual projections and datums? I understand the value of projections as output constructs, because of distortion, etc: that much is justifiable. However, I don't ...
tmcw's user avatar
  • 4,286
34 votes
3 answers
17k views

Which function for creating a POINT in PostGIS?

When defining a Point in PostGIS, when do you decide to use which of the following? ST_SetSRID(ST_MakePoint(lon,lat),4326) ST_SetSRID(ST_Point(long,lat),4326) ST_SetSRID(ST_GeomFromText('POINT(lon ...
Nyxynyx's user avatar
  • 1,687
34 votes
1 answer
9k views

How to create an accurate Tissot Indicatrix?

A Tissot Indicatrix is useful method for communicating at a glance the kinds of distortion a given projection is prone to (in the figure below, each of the red circles occupies the same area). I've ...
matt wilkie's user avatar
  • 28.2k
31 votes
9 answers
29k views

ArcCatalog says spatial references don't match between feature dataset and feature class with same coordinate system?

I have a feature dataset that is using the GCS_WGS_1984 as the geographic coordinate system. It includes a few feature classes. This feature dataset is itself in a file geodatabase that contains a ...
mindless.panda's user avatar
30 votes
2 answers
1k views

What projection appeared in the NYTimes this morning?

Perhaps not as GIS related as some, but definitely about maps. Can anyone identify the map projection that appeared in the New York Times this morning? It's not one I've seen before, and a quick scan ...
mattwigway's user avatar
  • 2,937
30 votes
2 answers
109k views

Understanding difference between Coordinate System and Projection?

Can somebody please explain what is the difference between the Coordinate system (WGS 84 for example) and a Projection (Universal Transverse Mercator for example)? What is the difference between a ...
marco's user avatar
  • 1,137
29 votes
6 answers
28k views

Defining projections for multiple shapefiles in ArcMap?

I have over 100 shape files that don't have .prj file and thus when I bring them into ArcMap 10 they show the coordinate system as unknown. I know all of the shape files coordinate system is GCS WGS ...
wilbev's user avatar
  • 1,709
29 votes
9 answers
37k views

Manually transforming rotated lat/lon to regular lat/lon?

First I should clarify I don't have previous experience with the field, so I don't know the technical terminology. My question is as follows: I have two weather datasets: The first one has the ...
skd's user avatar
  • 393
29 votes
1 answer
69k views

How to assign CRS to RasterLayer in R

I have a layer with coord. ref. : NA. How can I assign coord. ref. : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 to coord. ref. : NA? class : RasterLayer dimensions : 127,...
Nahm's user avatar
  • 861
29 votes
2 answers
10k views

Calculating areal distortion outside UTM zone?

One of my colleagues is working with data that is spread across two UTM zone. The majority of the data is in one zone, with a few outliers in another zone. He would like to know what the area ...
kenbuja's user avatar
  • 5,690
29 votes
6 answers
15k views

Dealing with data that spreads across UTM Zones?

I have data that spreads across two UTM Zones GDA/MGA94 UTM Zone 55 and 56. I have layers such as a cadastre, roads, pipelines etc where I want to store measurements like lengths and areas in metres ...
Ando's user avatar
  • 3,039
27 votes
3 answers
27k views

Get Lon Lat values from a GEOGRAPHY data type in PostGIS

After storing lon lat values as a GEOGRAPHY data type, how do I retrieve the individual lat lon values? Failed attempt: SELECT id, geog, ST_X(geog), ST_Y(geog) FROM locations; Error: No function ...
Nyxynyx's user avatar
  • 1,687
27 votes
1 answer
7k views

Calculating Flow Direction and Delineating Basins from Projected vs. Unprojected DEM Data [closed]

This is somewhat of a theoretical question stemming from some discussions with colleagues on the topic of implications with delineating basins with projected (e.g., Albers Equal Area) vs. unprojected (...
MapBlast's user avatar
  • 1,127
27 votes
4 answers
13k views

Calculating distortion on Equirectangular Projection

I am trying to calculate distortion so I can distort overlaying text and forms to precisely match an image of an equirectangular projection. How does one calculate the distortion at a given latitude ...
NCashew's user avatar
  • 375
26 votes
4 answers
30k views

Is it possible to reproject spatial data using SQL Server?

SQL Server takes an SRID when creating spatial data, but is it possible to retrieve with a different SRID translating the coordinates? For example, let's say I have a bunch of spatial polygons using ...
Rowland Shaw's user avatar
26 votes
4 answers
42k views

Is there any online tool for converting coordinates between different EPSG?

Every time I want to do conversion, I need to get into the console to run proj.4. Is there any online tools for converting coordinates between different EPSG?
Harold Chan's user avatar
  • 1,667

1
2 3 4 5
169